Search

We introduce in this work a unique parameter for the quantitative assessment of the intrinsic strength of the [pi] interaction between two monomers forming a complex. The new parameter is a local intermonomer stretching force constant, based on the local mode theory, originally developed by Konkoli and Cremer, and derived from the set of nine possible intermonomer normal vibrational modes. The new local force constant was applied to a diverse set of more than 70 molecular complexes, which was divided into four groups. Group 1 includes atoms, ions, and small molecules interacting with benzene and substituted benzenes. Group 2 includes transition metal hydrides and oxides interacting with benzene while Group 3 involves ferrocenes, chromocenes, and titanium sandwich compounds. Group 4 presents an extension to oxygen [pi]-hole interactions in comparison with in-plane hydrogen bonding. We found that the strength of the [pi] interactions in these diverse molecular complexes can vary from weak interactions with predominantly electrostatic character, found, e.g., for argon-benzene complexes, to strong interactions with a substantial covalent nature, found, e.g., for ferrocenes; all being seamlessly described and compared with the new intermonomer local mode force constant, which also outperforms other descriptors such as an averaged force constant or a force constant guided by the electron density bond paths. We hope that our findings will inspire the community to apply the new parameter also to other intermonomer [pi] interactions, enriching in this way the broad field of organometallic chemistry with a new efficient assessment tool. Key words: local mode analysis, intermonomer force constant, sandwich complexes, vibrational spectroscopy, Introduction Noncovalent interactions between monomers leading to complex formation is the topic of many experimental and computational investigations, because of the vital role they play in the structure and properties [...]

Cobalt-free manganese-based lithium-rich layered oxides (LLOs) have garnered research attention as prospective lithium-ion cathode materials owing to their large specific capacity and low price. However, their large-scale application is hindered by their low Coulombic efficiency, poor cycling performance, voltage attenuation, and structural phase transition. To address these issues, the LLO structure is modified via Ti doping at the manganese site herein. Ti-doped Li1.2Mn0.6−xTixNi0.2O2 (x = 0, 0.03, 0.05, 0.10, and 0.15) is prepared using the high-temperature solid-state method. The Ti-doped Li1.2Mn0.6Ni0.2O2 is calculated via first principles. The results show that Ti4+ doping improves the cycle stability and rate performance of Li1.2Mn0.6Ni0.2O2. Electrochemical test results show that the sample exhibits enhanced electrochemical performance when the Ti doping amount is 0.05. The discharge specific capacity at 0.1C is 210.4 mAh·g−1, which reaches 191.1 mAh·g−1 after 100 cycles, with a capacity retention rate of 90.7%. This study proves the feasibility of using cheap cobalt-free LLOs as cathode materials for LIBs and provides a novel system for exploiting low-cost and high-performance cathode materials. [ABSTRACT FROM AUTHOR]

We introduce in this work a unique parameter for the quantitative assessment of the intrinsic strength of the π interaction between two monomers forming a complex. The new parameter is a local intermonomer stretching force constant, based on the local mode theory, originally developed by Konkoli and Cremer, and derived from the set of nine possible intermonomer normal vibrational modes. The new local force constant was applied to a diverse set of more than 70 molecular complexes, which was divided into four groups. Group 1 includes atoms, ions, and small molecules interacting with benzene and substituted benzenes. Group 2 includes transition metal hydrides and oxides interacting with benzene while Group 3 involves ferrocenes, chromocenes, and titanium sandwich compounds. Group 4 presents an extension to oxygen π–hole interactions in comparison with in-plane hydrogen bonding. We found that the strength of the π interactions in these diverse molecular complexes can vary from weak interactions with predominantly electrostatic character, found, e.g., for argon–benzene complexes, to strong interactions with a substantial covalent nature, found, e.g., for ferrocenes; all being seamlessly described and compared with the new intermonomer local mode force constant, which also outperforms other descriptors such as an averaged force constant or a force constant guided by the electron density bond paths. We hope that our findings will inspire the community to apply the new parameter also to other intermonomer π interactions, enriching in this way the broad field of organometallic chemistry with a new efficient assessment tool. [ABSTRACT FROM AUTHOR]

The conformational properties of ring compounds such as cycloalkanes determine to a large extent their stability and reactivity. Therefore, the investigation of conformational processes such as ring inversion and/or ring pseudorotation has attracted a lot of attention over the past decades. An in-depth conformational analysis of ring compounds requires mapping the relevant parts of the conformational energy surface at stationary and also at non-stationary points. However, the latter is not feasible by a description of the ring with Cartesian or internal coordinates. We provide in this work, a solution to this problem by introducing a new coordinate system based on the Cremer–Pople puckering and deformation coordinates. Furthermore, analytic first- and second-order derivatives of puckering and deformation coordinates, i.e., B-matrices and D-tensors, were developed simplifying geometry optimization and frequency calculations. The new coordinate system is applied to map the potential energy surfaces and reaction paths of cycloheptane (C7H14), cyclooctane (C8H16), and cyclo[18]carbon (C18) at the quantum chemical level and to determine for the first time all stationary points of these ring compounds in a systematic way. [ABSTRACT FROM AUTHOR]

Conceptually mimicking biomolecules' ability to construct multiple‐helical aggregates with emergent properties and functions remains a long‐standing challenge. Here we report an atom‐precise 18‐copper nanocluster (NC), Cu18H(PET)14(TPP)6(NCS)3 (Cu18H) which contains a pseudo D3‐symmetrical triple‐helical Cu15 core. Structurally, Cu18H may be also viewed as sandwich type of sulfur‐bridged chiral copper cluster units [Cu6−Cu6−Cu6], endowing three‐layered 3D chirality. More importantly, the chiral NCs are aggregated into an infinite double‐stranded helix supported by intra‐strand homonuclear C−H⋅⋅⋅H−C dihydrogen contacts and inter‐strand C−H/π and C−H/S interactions. The unique multi‐layered 3D chirality and the double‐helical assembly of Cu18H are evocative of DNA. Moreover, the collective behaviours of the aggregated NCs not only exhibit crystallization‐induced emission enhancement (CIEE) and aggregation‐induced emission enhancement (AIEE) effects in the deep‐red region, but also efficiently catalyze electron transfer (ET) reaction. This study thus presents that hierarchical assemblies of atomically defined copper NCs could be intricate as observed for important biomolecules like DNA with emergent properties arising from aggregated behaviours. [ABSTRACT FROM AUTHOR]